As products get smaller and smaller, there is increased demand for micro-electrical-mechanical systems (MEMS), micro-optical devices and photonic crystals. With this demand, there is an associated increased interest in micro- and nano-machining. Numerous applications exist for MEMS. As a breakthrough technology, allowing unparalleled synergy between previously unrelated fields such as biology and microelectronics, new MEMS applications are emerging at a rapid pace, expanding beyond those currently identified or known. Additional applications in quantum electric devices, micro-optical devices and photonic crystals are also emerging.
Here are a few applications of current interest:
Quantum Electrical Devices
Interest in ideas such as quantum computing have led to the development of devices requiring increasing smaller dimensions, such as cellular automata and coupled quantum dot technologies. Resonant tunneling devices such as resonant tunneling diodes, which may utilize quantum effects of transmission electrons to increase the efficiency of microwave circuits, require particularly fine features.
Micro-Optics
The application of micro-machining techniques to optics has lead to numerous advances in optical fabrication such as gray scale technology. Gray scale technology allows for the creation of a wide variety of shapes allowing for the best optical performance achievable. Traditional binary optics rely on a “stair step” shaped approximation of the ideal surface shape. Gray scale can actually create that ideal shape. Curves, ramps, torroids, or any other shape is possible. Multi-function optics, microlens arrays, diffusers, beam splitters, and laser diode correctors may all benefit from the use of gray scale technology. These optical devices as well as others, including fine pitch gratings for shorter and shorter wavelength light, benefit from increased precision available using micro-machining. Optical MEMS devices including beam shapers, continuous membrane deformable mirrors, moving mirrors for tunable lasers, and scanning two axis tilt mirrors have also emerged due to progress in micro-machining technology.
Photonic Crystals
Photonic crystals represent an artificial form of optical material that may be used to create optical devices with unique properties. Photonic crystals have many optical properties that are analogous to the electrical properties of semiconductor crystals and, thus, may also allow the development of optical circuitry similar to present electrical semiconductor circuitry. The feature sizes used to form photonic crystals and the precise alignment requirements of these features complicate manufacture of these materials. Improved alignment techniques and reduced minimum feature size capabilities for micro-machining systems may lead to further developments in this area.
Biotechnology
MEMS technology has enabling new discoveries in science and engineering such as: polymerase chain reaction (PCR) microsystems for DNA amplification and identification; micro-machined scanning tunneling microscope (STM) probe tips; biochips for detection of hazardous chemical and biological agents; and Microsystems for high-throughput drug screening and selection.
Communications
In addition to advances that may result from the use of resonant tunneling devices, high frequency circuits may benefit considerably from the advent of RF-MEMS technology. Electrical components such as inductors and tunable capacitors made using MEMS technology may perform significantly better than their present integrated circuit counterparts. With the integration of such components, the performance of communication circuits may be improved, while the total circuit area, power consumption and cost may be reduced. In addition, a MEMS mechanical switch, as developed by several research groups, may be a key component with huge potential in various microwave circuits. The demonstrated samples of MEMS mechanical switches have quality factors much higher than anything previously available. Reliability, precise tuning, and packaging of RF-MEMS components are to be critical issues that need to be solved before they receive wider acceptance by the market.
Advances in micro-optics and the introduction of new optical devices using photonic crystals may also benefit communications technology.
Accelerometers
MEMS accelerometers are quickly replacing conventional accelerometers for crash air-bag deployment systems in automobiles. The conventional approach uses several bulky accelerometers made of discrete components mounted in the front of the car with separate electronics near the air-bag. MEMS technology has made it possible to integrate the accelerometer and electronics onto a single silicon chip at a cost of ⅕ to 1/10 of the cost of the conventional approach. These MEMS accelerometers are much smaller, more functional, lighter, and more reliable as well, compared to the conventional macro-scale accelerometer elements.
Micro-Circuitry
Reducing the size of electronic circuits is another area in which MEMS technology may affect many fields. As the density of components and connections increases in these microcircuits, the processing tolerances decrease. One challenge in producing micro-circuitry is preventing shorts between components and nano-wires which are located ever closer together. Yields may be significantly increased by micromachining methods with the capability to repair these defects.
Laser machining of surfaces using the near-field mode radiation of a near-field scanning optical microscope (NSOM), sometimes known as a scanning near-field optical microscope, has been proposed as a means of laser machining submicron features. One potential method for micromachining surfaces in this way is disclosed in Japanese Patent Application 2000-51975, LASER MACHINING APPARATUS AND ITS METHOD AND AN OPTICAL ELEMENT MACHINED BY USING SAME, to H. Owari, et al. Owari, et al. disclose using light from a short-wavelength ultraviolet laser that is transmitted through the probe of an atomic force microscope to laser machine an optical grating.
NSOM's use many of the same principles as atomic force microscopes (AFM's) to accurately profile surfaces. Laser micromachining of these surfaces using near-field radiation from an NSOM probe tip may provide a number of advantages compared to using non-near-field radiation and free space optics. The advantages may include precise positioning control of the NSOM probe tip and a reduced minimum feature size. The precise motion stages used in NSOM devices may be used to provide precise horizontal and vertical positioning control. Additionally, the ability of an NSOM to profile a surface allows for the accurate vertical positioning of the probe tip desired to couple significant near-field radiation to the surface. It is noted that other modes than the near-field mode may be transmitted through the NSOM probe tip, but, as long as the probe tip is maintained suitably close to the surface being machined, the possible presence of these other modes does not have a large effect on these advantages of NSOM laser machining.
The minimal feature size that may be machined with an exemplary NSOM laser machining system of the present invention is determined by the size of the NSOM probe tip, rather than by the wavelength of the laser light used to generate the near-field radiation. This may allow a laser machining apparatus, such as that disclosed by Owari et al., to machine areas on a surface, which are smaller than the diffraction limited spot size of a free space laser beam from the same laser source. The wavelength of the laser is still an issue, however, because it affects the efficiency with which the light may be coupled into the near-field through the NSOM probe tip. Thus, Owari et al. disclose the use of short wavelength UV lasers with wavelengths approximately equal to the diameters of the circular cross-sections of their NSOM probe tips.
An important issue in such a system is ensuring that the laser light is efficiently coupled into, and out of, the NSOM probe.
The tip of the NSOM probe is desirably formed to allow light in the near-field mode to be coupled through the probe tip, while substantially preventing light from being transmitted in the far-field mode. The probe tip may be imaged in a scanning electron microscope (SEM) and the tip quality assessed based on its appearance, but this method does not provide a direct measurement of the light coupled through the tip. Thus, it may be difficult, or even impossible, to calibrate the probe tips using SEM images only. Additionally, taking SEM images of the probe tip requires removing the NSOM probe from the NSOM. SEM imaging may be desirable to initially screen NSOM probes for defective NSOM tips, but it is impractical for monitoring of the probe tips during operation for wear and/or damage. Therefore, a means to measure the power of light coupled through NSOM probe tips, particularly the power of light coupled into the near-field mode, is desirable.